The present invention relates to a rectifying circuit. More particularly, the invention relates to a rectifying circuit having wiring patterns configured to have reduced resistance Rac. The invention also relates to a switching power supply device, and more particularly to a switching power supply device including a rectifying circuit having wiring patterns configured to have reduced resistance Rac.
Generally, the switching power supply device includes a switching circuit for converting DC input voltage into AC voltage, a rectifying circuit for rectifying the AC voltage converted, and a smoothing circuit which smoothes the output voltage from the rectifying circuit and generates a DC output voltage. The switching power supply device thus arranged is capable of generating an output voltage whose value is different from an input voltage. The rectifying circuit of the switching power supply device includes a pair of input terminals, a pair of output terminals and a plurality of rectifying elements. In the rectifying circuit, an AC voltage to be rectified is applied to the pair of input terminals, and an output voltage having a rectified waveform appears between the pair of output terminals.
FIG. 11 is a plan view schematically showing a circuit layout of a conventional rectifying circuit.
As shown in FIG. 11, the conventional rectifying circuit includes three first rectifying elements 1-1, 1-2 and 1-3 and three second rectifying elements 2-1, 2-2 and 2-3, and those rectifying elements are linearly arranged in this order. The first rectifying elements 1-1, 1-2 and 1-3 are connected in parallel between a first secondary side terminal 4 of a transformer 3 and a grand terminal 7. The second rectifying elements 2-1, 2-2 and 2-3 are connected in parallel between a second secondary side terminal 5 of the transformer 3 and the grand terminal 7. With this arrangement, the first and the second secondary side terminals 4 and 5 serve as a pair of input terminals of the rectifying circuit. A center tap 6 of the transformer 3 and the grand terminal 7 serve as a pair of output terminals of the rectifying circuit. In this arrangement, the first rectifying elements 1-1, 1-2 and 1-3 are connected in parallel and the second rectifying elements 2-1, 2-2 and 2-3 are connected in parallel. It is for this reason that the increase of the current drive capability of the rectifying circuit is intended.
A wiring pattern 10 is used for connecting the first rectifying elements 1-1, 1-2 and 1-3 to the first secondary side terminal 4 of the transformer 3. A wiring pattern 11 is used for connecting the second rectifying elements 2-1, 2-2 and 2-3 to the second secondary side terminal 5 of the transformer 3. A wiring pattern 12 is used for connecting the rectifying elements to the grand terminal 7. Those wiring patterns 10 to 12 are all formed on a surface of a printed circuit board.
The DC resistance Rdc between each of the rectifying elements and the related terminals connected thereto (the first and the second secondary side terminals 4 and 5, and the grand terminal 7) is given by
Rdc=Roxc3x97L/S
where
Ro: resistivity of each of wiring patterns 10 to 12
L: length of each of wiring patterns 10 to 12
S: cross sectional area of each of wiring patterns 10 to 12.
However, the conventional rectifying circuit thus arranged suffers from following problem. In the circuit, as a frequency of a current flowing through the rectifying circuit becomes high, an AC resistance Rac between the rectifying elements and the terminals connected there to becomes large. For example, in the circuit layout shown in FIG. 11, when a frequency of an AC voltage to be rectified is about 200 kHz, the AC resistance Rac is considerably large, e.g., three to four times as large as the DC resistance Rdc in value. As a result, such a problem arises that large loss is generated in the rectifying circuit, particularly in a high-frequency region.
Accordingly, an object of the invention is to provide a rectifying circuit having wiring patterns configured to have reduced resistance Rac.
Another object of the invention is to provide a rectifying circuit in which the rectifying elements are optimumly arranged.
Yet another object of the invention is to provide a switching power supply device having a rectifying circuit having wiring patterns configured to have reduced resistance Rac.
Still another object of the invention is to provide a switching power supply device having a rectifying circuit in which the rectifying elements are optimumly arranged.
According to one aspect of the present invention, there is provided a rectifying circuit having a pair of input terminals at which an AC voltage appears, a plurality of first rectifying elements, a plurality of second rectifying elements, a first wiring pattern for connecting one of the paired input terminals to the plurality of first rectifying elements, and a second wiring pattern for connecting the other of the paired input terminals to the plurality of second rectifying elements, wherein the plurality of first rectifying elements and the plurality of second rectifying elements are laid out so that at least two boundaries between the first and second rectifying elements adjacent to each other are present.
In the invention, the plurality of first rectifying elements and the plurality of second rectifying elements are laid out so that at least two boundaries between the first and second rectifying elements adjacent to each other are present. With such a layout of the rectifying elements, current flow paths between one of the input terminals and the plurality of first rectifying elements and current flow paths between the other of the input terminals and the plurality of second rectifying elements, are closely disposed. Therefore, AC resistance Rac in the first wiring pattern and the second wiring pattern is effectively reduced.
Preferably, the number of boundaries between the first and second rectifying elements adjacent to each other, is larger than the sum of the number of boundaries between the two first rectifying elements adjacent to each other, and the number of boundaries between the two second rectifying elements adjacent to each other.
In the preferred circuit mentioned above, AC resistance Rac in the first wiring pattern and the second wiring pattern is more effectively reduced.
Preferably, in the rectifying circuit, the plurality of first rectifying elements and the plurality of second rectifying elements are alternately arranged.
In another preferred circuit mentioned above, AC resistance Rac in the first wiring pattern and the second wiring pattern is more effectively reduced.
Preferably, in the rectifying circuit, the plurality of first rectifying elements and the plurality of second rectifying elements are substantially linearly arranged.
Still preferably, in the rectifying circuit, the plurality of first rectifying elements and the plurality of second rectifying elements are arcuately arranged.
In still another preferred circuit as mentioned above, the DC resistance Rdc per se in the first wiring pattern and the second wiring pattern is reduced, and hence the AC resistance Rac thereof is further reduced.
Preferably, the rectifying circuit further includes a pair of output terminals at which a voltage produced by rectifying the AC voltage, and a third wiring pattern for connecting one of the output terminals to the plurality of first rectifying elements and the plurality of second rectifying elements.
According to the preferred circuit as mentioned above, a current flow path between one of the output terminals and the plurality of first rectifying elements and a current flow path between one of the output terminals and the plurality of second rectifying elements, may be closely disposed. Therefore, the AC resistance Rac in the third wiring pattern is effectively reduced.
Preferably, in the rectifying circuit, the first wiring pattern is formed with of a plurality of first unit wiring patterns formed on a multi-layered circuit board, and the second wiring pattern is formed with a plurality of second unit wiring patterns formed on the multi-layered circuit board.
Preferably, in the rectifying circuit, the plurality of first unit wiring patterns and the plurality of second unit wiring patterns are alternately formed in the multi-layer circuit board.
According to the preferred embodiments as mentioned above, a current flow path between one of input terminals and the plurality of first rectifying elements and a current flow path between the other of input terminals and the plurality of second rectifying elements, are closely disposed in the horizontal and the vertical directions. Therefore, the AC resistance Rac in the first wiring pattern and the second wiring pattern is more effectively reduced.
According to another aspect of the present invention, there is provided a switching power supply device having a switching circuit for converting DC input voltage into AC voltage, a rectifying circuit for rectifying the AC voltage, and a smoothing circuit for smoothing output voltage from the rectifying circuit, the improvement being characterized in that the rectifying circuit includes a pair of input terminals to which the AC voltage is applied, a plurality of first rectifying elements, a plurality of second rectifying elements, a first wiring pattern for connecting one of the paired input terminals to the plurality of first rectifying elements, and a second wiring pattern for connecting the other of the paired input terminals to the plurality of second rectifying elements, wherein the plurality of first rectifying elements and the plurality of second rectifying elements are laid out so that at least two boundaries between the first and second rectifying elements adjacent to each other are present.
According to the invention, a current flow path between one of the input terminals and the plurality of first rectifying elements and a current flow path between the other of the input terminals and the plurality of second rectifying elements, may be closely disposed. Therefore, AC resistance Rac in the first wiring pattern and the second wiring pattern is effectively reduced. With this feature, in a case where the output current is large, or in a case where the switching frequency is high, the loss generated in the rectifying circuit is effectively suppressed.
Preferably, in the switching power supply device, the number of boundaries between the first and second rectifying elements adjacent to each other, is larger than the sum of the number of boundaries between the two first rectifying elements adjacent to each other, and the number of boundaries between the two second rectifying elements adjacent to each other.
Preferably, in the switching power supply device, the plurality of first rectifying elements and the plurality of second rectifying elements are alternately arranged.
Preferably, the rectifying circuit further includes a pair of output terminals connected to the smoothing circuit, and a third wiring pattern for connecting one of the paired output terminals to the plurality of first rectifying elements and the plurality of second rectifying elements.
Still preferably, the switching power supply device further includes a transformer having a pair of secondary side terminals and a center tap, wherein the paired input terminals of the rectifying circuit are connected to the paired secondary side terminals of the transformer, and the other of the paired output terminals of the rectifying circuit is connected to the center tap of the transformer.